This invention relates to proteins. More specifically, it relates to the modification of natural proteins to improve their functionality and thereby enhance their utility in food compositions.
Nutritional value is a primary concern in the world's quest for new sources of protein, but consideration must also be given to the protein's functional and flavor characteristics. For while nutritionally balanced foods may be prepared from a wide variety of sources, acceptability of such foods depends upon their sensory properties such as taste and texture. A protein substituted for traditional proteins should therefore maintain or improve the quality and acceptability of the food products in which it is incorporated. This requires that the new protein not only possess satisfactory nutritional properties, but also acceptable flavor, color and additional functional properties, such as solubility, thermal stability, emulsifying, foaming and texturizing characteristics.
At the same time, the food industry is seeking less expensive proteins for use in the preparation of modern convenience foods. In such uses, the protein often must have specific functional characteristics. For example, the protein in a coffee whitener should not precipitate when added to the coffee and a protein for use in carbonated beverages must be acid soluble.
It is therefore a primary objective of the present invention to provide a simple and inexpensive method of preparing functional protein for use in a wide variety of food compositions.
Prior attempts aimed at achieving such an objective include:
1. Direct enzymatic proteolysis of natural proteins such as taught in U.S. Pat. Nos. 2,489,208 and 3,889,001. This approach normally uses low levels of enzyme for extended reaction times. Yield of soluble functional protein from such processes is usually low and the product generally has poor flavor.
2. Enzymatic treatment of natural protein which has initially been subjected to high shear to modify the protein structure. As exemplified in U.S. Pat. No. 3,694,221, proteolysis of the pretreated protein is accomplished with high levels of enzyme for short reaction times and purportedly gives an easily wettable and dispersable product with good mouthfeel.
3. Enzymatic treatment of heat-treated protein such as disclosed in U.S. Pat. Nos. 3,857,966 and 3,876,806. In U.S. Pat. No. 3,857,966, heat-precipitated and separated protein is initially subjected to alkaline hydrolysis at elevated temperature and then to a sequential proteolytic hydrolysis which utilizes both microbial alkaline and neutral protease plus plant protease over a period of about two hours. U.S. Pat. No. 3,876,806 discloses a process in which an aqueous slurry of defatted vegetable seed protein is initially heat treated to destroy vegetative cells and then subjected to enzymatic proteolysis to produce soluble protein. Separation of water insolubles is made after rather than prior to the proteolysis, and the product therefore contains not only soluble protein but also water-soluble impurities present in the protein source material.